<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 给某个⽇期增加 N 天并输出 -->
    <script>  
        var Dater = new Date();
        var sava = prompt('请输入一个数值代表你所增加的天数');
        var time1 = new Date(((Dater/1000)+(sava*86400))*1000);
        var time2 = time1.getFullYear() + "/" + (time1.getMonth() + 1) + "/" + time1.getDate();
        alert(time2);
    </script>
</body>
</html>